My laboratory has described a new gene family in mammalian cells. Transcription of this gene family is coordinately induced by platelet-derived growth factor (PDGF) in Balb/c-3T3 cells. We have isolated five representative members of this gene family (which we term "competence") by molecular cloning techniques. We have shown that at least two proto-oncogenes (c-myc and c-fos) are contained within the family. Some if not all, of the competence gene products function as positive intracellular mediators of the growth response to PDGF. During the course of this work, we also observed rare gene sequences whose expression is suppressed by PDGF. We suspect that these gene products may function as negative growth regulators. Specifically, genes which are suppressed by PDGF may serve to initiate and maintain the Go growth arrest state. The research described in this application has three objectives. The first objective is isolation and molecular characterization of PDGF-suppressible gene sequences. The genes will be isolated as full length cDNA clones. Towards this end we have updated and improved the differential colony hybridization protocol used to isolate the original competence genes. The second objective is to identify the translation products of these PDGF-suppressible genes. We will express the genes in bacteria and raise antisera to the expressed proteins. These antisera will be used to determine the subcellular location of PDGF-suppressible proteins. The nucleic acid sequence of the genes will be determined and then screened for homologies to other genes using computer matching techniques. The final objective is to determine whether these PDGF-suppressible genes inhibit the mitogenic response of normal 3T3 cells to serum and serum growth factors. This objective will be approached by transfecting the genes into 3T3 cells under control of a steroid inducible promoter element.